An electroluminescence device is a light-emitting device using a luminescent phenomenon occurring while an electric field is applied to a substance, and can be roughly classified into an organic EL device based on an organic material including metal complexes such as alumiquinolinol or conjugated macromolecules such as polyphenylenevinylene, and an inorganic EL device based on an inorganic material such as zinc sulfide or aluminum oxide salts.
Since the inorganic EL device has excellent durability and low power consumption as compared to the organic EL device, it is expected that the inorganic EL device will be applied to an image displaying system such as a light and large flat panel display. Further, the inorganic EL device can be classified into a dispersion type EL device obtained by dispersing a luminescent material in an inorganic or organic binder, and a thin film type EL device using a thin crystal film of a luminescent material. Although each type of the devices can act as a light emitting device by applying direct current or alternating current, in general, the thin film type EL device is superior as a high brightness and low power consumption device.
Here, in order to prepare an image displaying system, luminescent materials exhibiting emission such as red, green, blue, or the like are necessary. In the prior art, it has been known that, since an inorganic EL device is fabricated based on a Group II-VI compound composed of Group II element and Group VI element, such as ZnS or SrS,
a material obtained by adding a small amount of Mn (manganese) to ZnS emits yellow-orange light (For example, see non-patent document 1.);
a material obtained by adding Tb (terbium) and the like to ZnS emits green light (For example, see non-patent document 2.); and
a material obtained by adding Cu (copper) and the like to ZnS emits blue light (For example, see non-patent document 3.).
In general, these materials can be obtained by a process for doping a small amount of metals into a base carrier, such as firing (For example, see patent document 1.), or further, by doping at the time of preparing particles in a liquid phase and the like (For example, see patent document 2.).
An inorganic EL device can be prepared by forming an electrode on each of opposing sides of EL materials, and it can exhibit a luminescent phenomenon inherent in the inorganic EL material used, when a predetermined voltage is applied between the two electrodes of the inorganic EL device.
However, from the above inorganic EL materials, it is difficult to obtain a light emitter having a color and an emission intensity available to an image displaying system.
Luminescent bodies having obtained so far have problems that they do not have sufficient luminance and that they have shorter lifetime than other illumination (patent document 3). Luminance may be increased by applying a higher voltage. However, lifetime of a light emitter tends to become short, depending on an increase of an applied voltage. Consequently, it is necessary to select either brightness or lifetime.    [non-patent document 1] Journal of Crystal Growth 169 (1996) p 33-39    [non-patent document 2] Applied Surface Science 244 (2005) p 524-527    [non-patent document 3] Journal of luminescence 99 (2002) p 325-334    [patent document 1] Japanese patent publication Kokai Hei08-183954    [patent document 2] Japanese patent publication Kokai 2003-73119    [patent document 3] Japanese patent publication Kokai 2002-241753